It seems that if you increase intelligence you also increase the computational cost of its further improvement and the distance to the discovery of some unknown unknown that could enable another quantum leap. It seems that you need to apply a lot more energy to get a bit more complexity.

I don't necessarily think it's true that you need to know an unknown unknown to reach a "quantum leap". This is a very qualitative reasoning about intelligence. You could simply increase the speed. Also, evolution didn't make intelligence by knowing some unknown unknown, it was a result of trial and error. Further intelligence improvement could use the same method, just faster.